How can I clear event subscriptions in C#?

c1 {
 event EventHandler someEvent;
}

class c1
{
event EventHandler someEvent;
ResetSubscriptions() {someEvent = null;}
}

const
  WM_Paint = 998;  // <-- "question" can be done by several talkers
  WM_Clear = 546;

type
  MyWindowClass = class(Window)
    procedure NotEventHandlerMethod_1;
    procedure NotEventHandlerMethod_17;

    procedure DoPaintEventHandler; message WM_Paint; // <-- "answer" by this listener
    procedure DoClearEventHandler; message WM_Clear;
  end;